The lid of a steel-making electric furnace is conventionally constructed of refractory bricks in an annular arched arrangement for removably covering the top of the furnace body.
The brick portion of the lid, which is exposed to high-temperature radiant heat within the furnace, is gradually worn away owing to the resulting thermal damage and spalling and must therefore be replaced by new bricks frequently. This leads to a reduced operation efficiency and an increased operation cost. The problem has become more serious in recent years because a greater quantity electric power is used for operation.
The above problem is attributable to the high-temperature storage of heat in the brick which is inevitable in view of the low heat transfer coefficient of the brick, so that it has been desired to reduce the area of the brick portion to the greatest possible extent. Thus, steel lids are proposed for use with electric furnaces.
Conventional steel lids for furnaces comprise divided sectorial segments each having a cooling water jacket which is made of steel plate and internally divided by partitions. Since the partitions are provided by welding, there is a limitation in reducing the width of the cooling water channel, consequently limiting the flow speed of the cooling water and the cooling efficiency.
Furthermore the welded portions of the partitions permit stagnation of the cooling water and therefore deposition of fur, resulting in increased flow resistance, an insufficient flow rate and reduced thermal conductivity. The segment is susceptible to thermal damage especially at the portions where the front panel thereof is held in contact with the partitions without being exposed to the water.